1. Field of the Invention
The present invention relates to a printer, and more particularly, to a piezoelectric type ink jet head which employs shearing force mode and a method for driving the same.
2. Description of the Prior Art
For example, Japanese Laid-Open Patent Publication No. 18054/1990 discloses a drive technique of a printing head by means of a shearing force mode which includes deforming a barrier of a channel-like pressure chamber by using a deformation caused by a shearing force of a piezoelectric element and projecting an ink caused by the resultant pressure elevation of the pressure chamber.
Japanese Laid-Open Patent Publication No. 263760/1986 discloses an on-demand type printing head which includes mounting an electro-deforming element on an upper plate of an ink chamber, deforming the upper surface of the ink chamber by a stretching action of the electro-deforming element and projecting an ink.
In the conventional driving circuit for a printing head by deforming a barrier of a pressure chamber using a shearing force mode of a piezoelectric element as described in Japanese Laid-Open Patent Publication No. 18054/1990, drivers are required for each of corresponding driving electrodes provided for a plurality of channels which form an ink injection pressure chamber, and thus suffers drawbacks such as an increase in cost and an increase in space of the driving circuit, although the head itself has an advantage in that it is suitable for decreasing costs when compared with other modes. If a time-sharing drive mode which is disclosed in Japanese Laid-Open Patent Publication No. 263760/1986 is adopted so as to overcome the above-described defects, the structure of the head becomes a serial circuit of capacitators 703 as shown in FIG. 10(b) when pressure chambers of channels 701 have injection holes 702 as shown in FIG. 10(a). The equivalent circuit of a plurality of piezoelectric elements which forms the other type piezoelectric ink injection head becomes a parallel circuit of capacitators 901 having two terminals as shown in FIG. 12 and, if one side of each of the electrodes is connected to each of group drivers 911, 912, 913 as a common electrode of each group and the other side of each electrode is connected to each of channel drivers 921,922, and 923, each of which corresponds to the arrangement order in each group, and a group selection signal is added to a signal-input terminal of each group driver and a printing signal of the group is added to a signal-input terminal of each channel driver, ink injection operations corresponding to each printing signal of the each groups can be sequentially driven in a time-sharing manner in which the group number is n. To render time-sharing drive as described above, it is necessary to reconcile commonness and independence of electrodes group by group. However, if electrodes are connected with each other and are made common in a serial circuit of capacitors shown in FIG. 10(b), each independent drive becomes impossible and time-sharing drive becomes difficult. Thus, in this case, the drivers 705 are required which correspond to the number of driving electrodes 704. In a case of using a shearing force mode, a technique is also known which comprises alternatively arranging a channel J having an injection hole and a dummy channel D without having an injection hole as shown in FIG. 11(a). The equivalent cuircuit is made to a serial circuit of capacitators 803 as shown in FIG. 11(b) and is made to a common electrode by connecting a dummy electrode 804 and thus it can be independently driven in each driving electrode. But, if the common dummy electrode is sheared in any portion, a loop of charging and discharging between the dummy electrode and its adjacent driving electrode 802 is cut off and the barrier 803 of this part is made impossible to drive and thus time-sharing drive is made impossible. In addition, the conventional time-sharing drive mode has a defect in that printing dot pitch in a vertical direction is made ununiform due to the unevenness of the distances between adjacent injection holes which correspond to a phase difference of timings of injection from the injection holes, each of which belongs to different groups.